1. Field of the Invention
The present invention relates to metal vapor laser devices composed of a set of tubes containing metal to create the laser effect. Electrodes are placed at the two ends of an internal tube, and a pulsed electrical discharge is set up between these electrodes by means of a suitable electricity power supply. This discharge heats this medium between the electrodes, and an injected reactive gas then forms a volatile compound with the metal to be vaporized. The resulting atomic metallic vapor is also excited by the discharge and is subjected to population inversion which is the cause of the laser effect.
2. Description of Related Art
A number of examples of metal vapor laser devices are known, for example metallic halide lasers.
One such laser device is described in document GB-2 219 128. This device comprises an enclosure containing two electrodes and cylindrical metal segments, for example, made of copper or gold. During operation, a halogen gas (for example, bromine mixed with a helium buffer gas) circulates through the enclosure, and a metallic halide (for example, CuBr or Cu.sub.3 Br.sub.3) is produced. When the discharge takes place between electrodes, the metallic halide is vaporized and dissociates to form copper vapor which is then excited to produce a population inversion.
Another device is described in document U.S. Pat. No. 5,339,327. This device comprises a laser tube closed by two windows at its ends, and two electrodes placed inside it. One or several chambers or reaction vessels placed outside the tube contain metal, for example, copper in granular form. Neon and a halogen gas are allowed into this chamber. A coil surrounds the chamber and heats the metal contained in it. When the gas passes the coil, a metal halide is formed which vaporizes due to heating. The assembly is then inserted in the laser tube followed by dissociation of the metal halide and excitation of resulting products causing a population inversion.
A third device is described in the article by D. R. JONES et al. entitled "A high-efficiency 200 W average power copper HgBrID laser", which appeared in the IEEE Journal of Quantum Electronics, vol. 30, No. 10, p. 2385-2390, October 1994.
This device comprises a silica tube inside which there is an alumina tube. A copper anode and cathode, both cylindrical, on each side of this tube create a discharge. A mixture of Ne and HBr is added, the gas inlet being located on the same side as the anode opposite the side facing the alumina tube. Similarly, the gas outlet is on the same side as the cathode opposite the side facing the alumina tube.
In still other known devices, the gas is mixed before it reaches the laser, the active gas usually being introduced between the anode and the nearest window. Everything that remains of the gas after the discharge and the laser effect is extracted from the other side, between the cathode and the other window. Consequently, before entering the internal tube, the active gas passes through an electrode which necessarily includes high temperature zones in which it may react or decompose. The consequence of this is a high consumption of reactive gas (the third document mentioned above gives a consumption of the order of 3 to 4 normoliters/hour), and a reduction in the life of components, particularly of electrodes exposed to the reactive gas. The composition of this vapor phase is modified, and it may even be polluted by corrosion products.
Furthermore, the active gas reacts with metal, therefore its composition changes as it passes along the internal tube. Consequently, the metal halide concentration may have a high longitudinal gradient inside the tube.